kkh00116 CH13.indd Page 368 8/21/08 4:51:15 PM ... · Forensic Entomology Chapter 13 368 ... presentation, which is an overview of the chapter. It can be used as introductory material

ObjectivesAfter reading this chapter, you will understand:

• The stages of death.

• The role insects play in the decomposition of carrion.

• Postmortem interval.

• How insects can be used to estimate postmortem interval.

• The life cycle of insects.

• How variables affect results of scientifi c experiments.

You will be able to:

• Distinguish among major insect types associated with carrion.

• Identify the relationship between insect type and the stages of death.

• Perform the same experiments that forensic entomologists do.

• Estimate time of death from case description.

• Rear fl ies from pupae and larvae to adult.

• Explore variables affecting the determination of time of death.

Forensic Entomology

Chapter 13

368

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“When I was young I used to waitOn master and hand him his plateAnd pass the bottle when he got dryAnd brush away the bluetail fl y

One day he ride around the farmThe fl ies so numerous they did swarmOne chanced to bite him on the thighThe devil take the bluetail fl y

The pony run, he jump, he pitchHe threw my master in a ditchHe died and the jury wondered whyThe verdict was the bluetail fl y

They lay him under a ’simmon treeHis epitaph is there to see‘Beneath this stone I’m forced to lie

A victim of the bluetail fl y!’”

—from early American folk song, “Jimmy Crack Corn and I Don’t Care”

369


Use the handout provided by your teacher to record your answers.

1. What is a bug?

a) an insect b) a pest

c) a hidden microphone d) any or all of the above,

depending on who you are

talking to

2. A person who studies insects is an:

a) etymologist. b) insectologist.

c) entomologist. d) erythologist.

3. Insects are the most numerous living things on earth: true or false?

4. Taxonomy is:

a) the science of taxicabs. b) the classifi cation of things.

c) a book in the Bible. d) income tax evasion.

5. What is the proper name for insects with a hard, outer-body casing

and jointed legs?

a) arthropods b) snails

c) mammals d) lobsters

6. Most insects live on land: true or false?

7. The three basic body parts of an insect are:

a) head, eyes, tail. b) head, wings, legs.

c) head, abdomen, wings. d) head, thorax, abdomen.

8. How many legs does an insect have?

a) four b) six

c) eight d) any of the above

9. All adult insects have four wings: true or false?

10. Which is not an insect?

a) spider b) ant

c) bee d) beetle

11. Metamorphosis is:

a) a change in the body of insects. b) Sting’s new CD.

c) the middle earth. d) a process of extraterrestrial

travel.

12. Larva is:

a) a Hindu god. b) a volcanic rock.

c) the immature stage of d) a skin disease.

insect development.

Activity 13.1 Test Your Knowledge of the Insect World

More than likely, the “bluetail fl y” was a horsefl y.

Teacher Note

The TRCD for this chapter

includes a PowerPoint

presentation, which is an

overview of the chapter. It can be

used as introductory material or

at the end as a review.

The TRCD also contains a

crossword puzzle that can be

used after students have learned

the vocabulary from the end of

this chapter.

Teacher Note

The fi rst two activities of

this chapter can be skipped

depending upon time and prior

knowledge. Some of the activities

as written are dependent upon

climate. Using purchased pupae

and larvae can circumvent natural

conditions, but exploration is

not as exciting. The activities

can also take weeks to months,

depending on temperature, so

plan accordingly. The different lab

activities can also be performed

simultaneously to save time.

For these reasons, estimating a

time frame for completing this

chapter, or even each lab activity,

is problematic; however, we have

tried (see the Estimated Time

Charts in the TRCD).

Advance Preparation

Make copies of Blackline Master

13.1 from the Teacher Resource

CD to hand out to students.

370 Chapter 13

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13. Exoskeleton is:

a) the outer structure of b) the tough outer covering

a spacecraft. of insects.

c) X-man’s skeleton. d) bones found in the woods.

14. Hypothetically, if a pair of housefl ies bred in April, and all the

offspring lived, how many fl ies would there be by August?

a) 105 b) 1010

c) 1015 d) 1020

15. Label the parts of this housefl y as indicated in the diagram:

16. Label the parts of this beetle as indicated in the diagram:

Activity 13.1, continued

It is estimated that there are 300 million insects for each person on earth!

The common housefl y is

a major transmitter of

diseases such as typhoid

fever, conjunctivitis,

poliomyelitis, tuberculosis,

anthrax, leprosy, cholera,

diarrhea, and dysentery.

Answers

1. any or all of the above;

2. entomologist; 3. true;

4. the classifi cation of things;

5. arthropods; 6. true; 7. head,

thorax, abdomen; 8. six; 9. false,

they have two wings; 10. spider;

11. a change in the body of

insects; 12. immature stage of

insect development; 13. tough

outer covering of insects; 14. 1020;

15. Insects’ compound eyes are

made up of many hexagonal

lenses; insects have two

segmented antennae which are

used for smell and balance; all

adult insects have six legs; legs

and wings attach to the thorax;

abdomen is the segmented

tail area; 16. The elytron (plural:

elytra) is a hardened forewing

that protects the longer hind

wings in beetles; beetles have

two hind wings used for fl ying;

they can be folded under the

elytra when not in use. Although

the students may not be able to

answer some of the questions, this

exercise can provoke a discussion

about insects and their role in our

lives (e.g., spreading diseases;

being on the low end of the food

chain; and, most germane to

this chapter, as nature’s trash

recyclers).

eye

head

thorax

abdomen

antenna

leg

wing

wing

antenna

leg

eye

abdomen

thorax

head

elytron

371Forensic Entomology


Collection and Observation of Insects

A Berlese funnel is used to separate macrofauna from collected

soil samples. Different types of organisms can be examined with a

stereomicroscope, and perhaps some can be identifi ed.

Materials• Berlese funnel, either purchased or constructed from a large,

6- to 8-inch-wide funnel; galvanized screen with 1/8- to 1/4-inch mesh; and cheesecloth. Cut the screen with tin snips into a round disc that will fit snugly about two-thirds of the way down into the throat of the funnel. Line the mouth of the funnel with a single layer of cheesecloth and press it down so that it lies on top of the screen. The cheesecloth should drape over the funnel’s top rim (see Figure 13.1).

LaboratoryActivity 13.1

• ring stand to hold funnel and lamp

• vial wider than funnel stem filled one-half full with rubbing alcohol (70 percent isopropyl alcohol) and a few drops of glycerin to retard evaporation

• stereomicroscope • forceps or tweezers• trowel or spoon to collect soil

samples• plastic ziplock bags, 1 gallon• marking pen • 15-cm ruler • lamp with a 40- or 60-watt bulb

Figure 13.1 Berlese funnel

lightbulb

soil

screen

cheesecloth

collecting vialwith alcohol

funnel

There are 1,462 recorded

species of edible insects.

A few treats:

Thailand – bee grubs in

coconut cream

Laos – dragonfl y nymphs

United States – locust stew

Philippines – parched

locusts

Japan – boiled wasp larvae

South Africa – deep-fried

mopani worms

And a favorite – mealworm

chocolate chip cookies

macrofauna:

animals visible to the

naked eye, generally

1 mm and longer

Teacher Note

The purpose of this activity is

to acquaint the students with

the vast numbers of organisms

that live in the soil, as well as to

familiarize them with methods

of collection that are used by

forensic entomologists at the site

of a corpse.

The heat from the light and

drying of the soil drives the

animals down into the funnel.

Test this by turning off the light,

or keeping it on but also keeping

the soil moist. The sampling

environment could be changed

by adding wet leaves or placing a

board on the ground for several

days before sampling. Both

should increase populations.

Different organisms may inhabit

deeper layers, and in lesser

numbers.

372 Chapter 13

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Procedure

1. Collect soil samples; start with one about 6 inches square, 1 inch deep. Different lab groups should collect from different areas.

2. Place the sample in a plastic bag. Label it with date; group or student identification; description of the collecting site, including whether it was in shade or partial/direct sun; whether it is moist or dry; and type of soil (sandy, clay, organic, etc.).

3. If the sample is very wet, let it dry overnight in a cardboard box lined with newspaper. It may still be damp the next day.

4. Place the soil sample on top of the cheesecloth in the funnel. (No need to remove twigs, leaves, grass, etc.)

5. Place the collecting vial with alcohol beneath the funnel stem. 6. Turn on the light and watch what happens. Make daily records of the number

of specimens that fall into the collecting vial. 7. After a day or two, pour off the alcohol, use forceps or a toothpick to

remove specimens, and observe them with the stereomicroscope. Measure each organism and sketch it in your notebook. The chart below (Table 13.1) can serve as a model. Do not write in the textbook!

The types of organisms will vary according to the habitat. You may find ants (Hymenoptera), pillbugs (Isoptera), beetles (Coeloptera), cockroaches (Blattodea), earwigs (Dermaptera), springtails (Collembola), and immature insects that are difficult to identify, as well as earthworms, mites (Arachnida), spiders (Arachnida), and even centipedes

Laboratory Activity 13.1, continued

Table 13.1: Soil Specimens

No. Found

No. of Body Segments

No. of Pairs of Legs

No. of Pairs of Wings

Common Name

Class & Order

12

3

4

5

6

Teacher Note

Table 13.1 is reproduced as

Blackline Master 13.2 on

the TRCD.



(Chilopoda) and millipedes (Diplopoda). Figure 13.2 depicts a few of these insects.

springtail, <5 mm,beetle,

10–20 mmpillbug, extended

and coiled, to 14 mmearwig,

mite, <1 mm silverfish,12–25 mm

cockroach,10–15 mm

ant, 5–10 mm,

Figure 13.2 Common soil macrofauna

dichotomous:

“divided into two parts”;

therefore, dichotomous

keys always give two

choices in each step in

identifying an organism

“On my return to the

laboratory [from the crime

scene] . . . I put the soil

samples into Berlese

funnels to extract the

arthropods.”

—From M. Lee Goff’s A Fly

for the Prosecution, p. 82

Taxonomy

Carl Linnaeus (1707–1778) is credited with devising an orderly system of classifi cation which has been especially useful in the organization of biological systems. This method of classifi cation is called taxonomy and is applicable to many different systems. Linnaeus established conventions to impart a unique name for every living species. How does this work?

A kingdom is the broadest category; it is subdivided into a smaller unit, phylum, and so forth until we come to species, which is assigned a unique name.

Taxonomy of modern humans:

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Primates

Family: Hominidae

Genus: Homo

Species: sapiens

taxonomy: the classifi cation

of things in an orderly way that

indicates natural relationships


8. If you want to go further in identification, use a dichotomous key for insect orders, available from your teacher or online at http://earthlife.net/insects/orders-key.html or www.amnh.org/learn/biodiversity_counts/ident_help/Text_Keys/text_keys_index.htm.

9. Compare your data with those of other groups. Is there a relationship among collection site, type of soil, and other factors? What do you think caused the animals to leave the soil in the funnel? How could you test your hypothesis?

Teacher Note

Blackline Master 13.3 from the

Teacher Resource CD contains a

Dichotomous Key.

374 Chapter 13


We are especially interested in arthropods, especially beetles (Coleoptera) and fl ies (Diptera), as you will learn shortly. Let’s take a look at the classifi cation of a particular beetle that eats carrion:

Kingdom: Animalia

Phylum: Arthropoda (arthropods)

Class: Insecta (insects)

Order: Coleoptera (beetles)

Family: Silphidae (carrion beetles)

Genus: Nicrophorus

Species: humator

What does all this have to do with forensic science? Forensic entomology is the use of insects and other arthropods to aid in legal investigations. There are three general areas of application: urban entomology, affecting man and his environment (e.g., insect damage to structures); stored products entomology, such as insects infesting foodstuffs; and medicolegal entomology (or forensic medical entomology), which deals with necrophagous (carrion–feeding) insects that typically inhabit human remains. This is the subject that will occupy the rest of this chapter, particularly as it relates to the determination of the postmortem interval (PMI) associated with the time of death.

Species

Genus

Family

Order

Class

Phylum

Kingdom

Figure 13.3 The steps of taxonomy

arthropods: animals

characterized by jointed legs,

a segmented body, and a hard,

nonliving exo- (outer) skeleton.

The exoskeleton does not keep up

with the growth of the insect, and

so must be shed periodically. This

process is called molting. The stages

between molts are termed instars.

carrion: the carcass of a dead

and decaying animal

entomology: the scientifi c

study of insects

necrophagous: feeding on

carrion; from the Greek word phagos,

to eat, and necro, meaning dead

postmortem interval (PMI): the time elapsed since a

person has died

GO TO www.scilinks.org

TOPIC classification systems

CODE forensics2E375



To solve a crime, investigators must answer the fi ve “W’s”: Who was the victim, and/or the perpetrator; what happened; when did it happen; where did it happen; and why did it happen?

The Process of Death

Let’s look at death in order to relate it to various methods of estimating when it occurred. Realize that death is a process, not an event. Different

tissues and organisms in a living body die at different rates. For example, brain cells deprived of oxygen die within 3–7 minutes, whereas skin cells can live up to 24 hours. Even the defi nition of “death” varies within the legal and medical fi elds, especially now when a person can be on life-support systems.

Physical Methods of Determining Time of DeathA pathologist usually determines the time of death. It is most accurate if the body is found within the fi rst 24 hours after death, using the indicators

of algor mortis, livor mortis, and rigor mortis. After that time period, other methods must be employed; estimations are made by studying the environmental conditions and other information regarding the scene.

Algor mortis refers to the cooling rate of the body after death. Immediately upon death, the body can no longer metabolically maintain its temperature of 98.6�F (37�C) and begins to equalize its temperature to that of its environment. Measuring the internal body temperature can give some indication of the time of death, theoretically following Newton’s law of cooling, which states that the rate of change of the temperature

of an object is proportional to the difference between its own temperature and the ambient temperature (i.e., the temperature of its surroundings). This can be expressed mathematically by a simple fi rst-order differential equation:

dy � rydt or dT

� �K (T � TS)dt

This method of measurement was used for some time, but it applies only to small, inorganic substances, so it works with hot coffee or a pizza

The cause of death usually is quite obvious, especially to a medical examiner or forensic pathologist. The manner of death usually requires detective work as to what happened. For example, the corpse’s lungs are full of water: The cause of death is drowning; the manner of death could be accidental, suicide, homicide, natural (pulmonary edema), or undetermined.

algor mortis: the cooling of

body temperature after death

Temperature conversions:

�C � (5/9) � (�F � 32)

�F � (9/5) �C � 32

Most animals and plants are known only

by their genus and species names. Genus

name is spelled with a capital letter,

whereas the species name is normally

spelled with a small letter; in printed text

the pair are normally written in italics.

Teacher Note

For a nice little applet showing

the exponential decay and

effect of K, see http://orion.

math.iastate.edu/algebra/sp/

xcurrent/applets/cooling.html.

376 Chapter 13


coming out of the oven, but not for corpses. In some instances, the temperature of the corpse remains the same for a while or even rises due to reactions in cells as they shut down, as well as by bacterial generation of heat. Simpler to apply than Newton’s exponential temperature decay, and more accurate, is the Glaister equation:

Hours since death � 98.4�F � internal body temperature

1.5

This equation can be used from one to 36 hours after death, but is most accurate within the fi rst 12 hours. Generally, a body cools about 1–11∕2 degrees Fahrenheit per hour until it reaches ambient temperature. Consideration must be given to the temperature of the environment, type of clothing on the body, wetness of the clothing, air movement, how many layers of clothing, and other conditions. Also, the greater the ratio of surface area to mass, as with children or smaller adults, the faster the body cools.

Glaister equation: a

formula used for determining the

approximate time period since

death based on body temperature

The Potato Corpse LaboratoryActivity 13.2

Materials• several large baking potatoes

of different sizes• several large sweet potatoes of

different sizes

• a large beet• a large baking apple• microwave oven• thermometer

Procedure

1. Weigh each item and record the dimensions.2. Heat each food product in a microwave. Prick them prior to heating to let steam

escape. The beet and apple should be placed in a tray to catch any juices.

Teacher Note

Graph paper can be found on the

TRCD as Blackline Master 13.4

for use in this activity. See if any

student thinks of wrapping the

hot potato corpse in “clothing”

such as a cloth napkin, or

cooling the corpse with a blower,

or laying it on a conducting

versus insulating surface, etc.

You may also wish to give the

students a prepared hot potato

and have them estimate time of

death, with error limits.

For advanced students in

chemistry, this experiment can

be used to illustrate, or lead into,

the concept of heat capacity. See

www.ausetute.com.au/heatcapa.

html for a simple tutorial, and

www.chm.davidson.edu/

ChemistryApplets/calorimetry/

Specifi cHeatCapacityOfCopper.

html for an experiment to

determine heat capacity (in

this case copper, but it can be

applied to a potato).




3. Remove the product and insert a thermometer into the center. It will take a little practice to get the internal temperature to around 100°F.

4. Record room temperature and the temperature of the “body” as a function of time.5. Graph your results in your science notebook.

Analysis Questions

1. Describe the data mathematically.2. Compare results from the different materials with your classmates.3. Explain any differences.4. How reproducible are the results?5. What other variables could be explored?

livor mortis: a purple or red

discoloration of the skin caused by

pooling of blood after death

rigor mortis: a stiffness in

the muscles that occurs shortly

after death

Livor mortis refers to the pooling of blood in the body due to gravity after the heart stops. It appears on the skin as a purplish-red discoloration and can give an indication of the position of the body at the time of death. It does not occur in the areas of the body that are in contact with the ground or constricted by other objects, as the capillaries are compressed in those places. Livor mortis begins within a half hour after death and is most evident within the fi rst 12 hours. After this time, the discoloration of livor mortis will not move regardless of how the body is disturbed. This fact can

be useful in determining whether a body has been moved after death.

Rigor mortis refers to the rigidity of the skeletal muscles after death. Immediately upon death muscles begin to relax; ATP (adenosine triphosphate, an enzyme in the muscles) begins to break down, fl uid concentrations change, and the muscles become

rigid. Rigor mortis begins in the smaller muscles so is fi rst observed in the face, neck, and jaw. The noticeable stiffness of rigor mortis can occur

Extract from JonBenet Ramsey’s autopsy report

378 Chapter 13


within a few hours of death and is gone within approximately 30 hours, leaving the body limp. The effects of rigor mortis begin to disappear in the same order in which they began, the small muscles becoming limp fi rst, and then the larger muscles of the trunk, arms, and legs. Rigor mortis is affected by environmental conditions such as temperature, dehydration, condition of muscles, and their use prior to death; hence there are uncertainties in determining the time of death from rigor mortis also.

The observations in Table 13.2 may be used in estimating time of death, but must be used with caution:

Table 13.2: Rule of Thumb in Estimating Time of Death

Temperature of Body Stiffness of Body Time Since Death

warm not stiff not dead more than 3 hours

warm stiff dead between 3 and 8 hours

cold stiff dead between 8 and 36 hours

cold not stiff dead for more than 36 hours

Activity 13.2

A body, quite stiff, has been found lying on the fl oor in the basement of

a tenement building. Body temperature is measured to be 86°F; lividity

(discoloration) is not complete. The police want you, as medical examiner,

to estimate the time of death. You have available to you a study done on

114 natural deaths in 1872 (see Figure 13.4). Justify your conclusion.

How accurate is it? What factors could affect your opinion?

Estimating Time of Death

Hours

Perc

ent

of D

eath

s

100

90

80

70

60

50

40

30

20

10

01 2 3 4 5 6 7 8 9 10 11 12

Figure 13.4 Time for the onset of rigor mortis

Teacher Note

Livor mortis not set, �12 hours;

temperature change 12�F/1.5�F

� 8 hours (Glaister equation);

rigor mortis complete, so

consistent with data from

Figure 13.4. All methods are

approximate and depend on

such variables as ambient

temperature, air movement, body

size, age of the victim, etc. The

three indicators are consistent

with a PMI of 8, ±1 hour. See

Table 13.2.



Within four minutes of death, decomposition begins. Cells are deprived of oxygen, carbon dioxide in the blood increases, pH decreases, and wastes accumulate, poisoning the cells. Enzymes dissolve cells from the inside out, causing them to rupture, releasing fl uids. This entire process is termed autolysis.

Autolysis is fi rst observed after a few days by the appearance of fl uid-fi lled blisters on the skin and skin slippage where sheets of skin slough off areas of the body.

Putrefaction is the next step of decomposition. It is the destruction of the soft tissues of the body, primarily by bacteria. Usually the fi rst visible sign of putrefaction is a greenish cast to the skin. Gases such as methane and ammonia, released by continued decomposition of tissues, cause bloating. The odor of volatile butyric and propionic acids is unpleasant. Further decay of proteins and fats yields such interesting and odoriferous compounds as skatole, methyl disulfi de, and the aptly named cadaverine and putrescine. By this time, the body is a mass of fl uids and smells just awful. Some call this stage “black putrefaction.” (See Table 13.3.) The stages are continuous; the times are for general reference and are dependent upon many variables.

autolysis: a process by which a

biological cell self-destructs

putrefaction: the

decomposition of animal

proteins, especially by anaerobic

microorganisms

Table 13.3: The Stages of Decomposition

Stage Description

Initial or fresh decay (autolysis)

The cadaver appears fresh externally but is

decomposing internally due to the activities of

bacteria present before death (0–4 days).

Putrefaction or bloating

The cadaver is swollen by gas produced internally,

accompanied by the odor of decaying flesh (4–10 days).

Black putrefaction Flesh of creamy consistency, with exposed body parts

black. Body collapses as gases escape. Fluids drain

from body. Odor of decay very strong (10–20 days).

Butyric fermentation Cadaver drying out. Some flesh remains at first;

cheesy odor from butyric acid (20–50 days).

Dry decay (diagenesis)

Cadaver almost dry; slow rate of decay. May

mummify (50–365 days).

skatole

N

H

CH3CH2COOHpropionic acid

CH3CH2CH2COOHbutyric acid

H2NCH2CH2CH2CH2NH2

putrescineH2NCH2CH2CH2CH2CH2NH2

cadaverine

380 Chapter 13


Adipocere formation sometimes occurs months to years after death. Adipocere is usually a yellowish-white, greasy, waxlike substance that forms as a result of the saponifi cation of fatty acids, most often catalyzed by a particular anaerobic bacterium. Conditions most favorable to its formation are burial in a moist, alkaline soil (which retards putrefaction and scavengers), high body fat of the corpse, and burial in a casket within a burial vault. This process helps to preserve the body, which may aid in identifi cation and recognition of injuries. (For a fascinating mystery involving this subject, read Carved in Bone by Jefferson Bass.)

Mummifi cation is the result of dehydrated tissue, usually skin, that has survived decay. It commonly develops under hot, dry conditions with persons of low body fat and can occur as early as one month after death.

In the fi nal stage, bone is chemically altered, especially by moisture and the pH of soil. This process is called diagenesis.

The rate of decomposition depends on many variables; most important are the environment, temperature, and the presence of scavengers. For example, a body decays twice as fast underwater and half as fast underground. The following equation gives a very rough estimate for time of decomposition of soft tissue for a person lying on the ground:

Number of days to become skeletonized � 1,285

average temperature, ºC

Thus, if the average temperature around the corpse is 20ºC (68ºF), it will take about 64 days to leave only a skeleton. In the tropics, at an average temperature of 30ºC, it would take only 30 days or less because of the higher humidity. This gives investigators a ballpark time frame with which to begin their investigation.

adipocere: also called “grave

wax,” insoluble fatty acids left as

residue from preexisting fats from

decomposing cadavers. It is formed

by the slow hydrolysis of fats in

wet ground and can occur in both

embalmed and untreated bodies.

saponifi cation: the alkaline

hydrolysis of fatty acid esters. In

chemistry, it refers to the reaction

of a base with a fat to form soap.

diagenesis: the process of

chemical and physical change

in deposited sediment during its

conversion to rock

13.1: Colonel William Shy

An interesting anomaly occurred when Dr. Bill Bass, of Body Farm

fame, was called to investigate an apparent defi ling of the grave of a

Confederate colonel, William Shy, who was killed in 1864. The

disturbed grave was thought to contain a recent burial. The hole had

presumably been dug by those who dumped the body; the cast-iron coffi n

had also been broken open. On top of the coffi n, Dr. Bass found the body



Many insects are carrion eaters. Indeed, if it weren’t for them, our forests and meadows would be full of animal parts. The life cycle of insects is

well known. For example, the four principal stages of metamorphosis of a fl y are: (1) egg; (2) larva (maggot); (3) pupa (plural, pupae); (4) winged adult.

Figure 13.5 shows the detailed life cycle of the common housefl y (Musca domestica).

The female fl y deposits 100–150 eggs at a time. They hatch as larvae, which eat a lot and grow fast. With a somewhat rigid exoskeleton, they must molt. The fi rst larval stage is called the fi rst instar; the second, the second instar. The third instar is the longest. By this time, the larva is full and no longer interested in eating. It becomes restless and moves away from the food source. It is now in its prepupal stage, during

of a large man, dressed in a tuxedo, decayed, but with fl esh of a pink, healthy

color. Judging from the state of the decayed fl esh and the odor, Dr. Bass

estimated the time since death to be six to 12 months.

However, there was no other body in the grave.

After comparing the body’s physical dimensions to

those of Colonel Shy, and considering the method of

embalming bodies in the mid 1800s, the teeth, and

the type of clothes on the corpse, Dr. Bass came to

the conclusion that the corpse was indeed Colonel

Shy, right where he was supposed to be. The body

was 113 years old, not 12 months! Apparently,

the lead-lined coffi n and embalming method

(using arsenic compounds) had prevented normal

decomposition beyond autolysis which had occurred

prior to burial. The disturbance at the grave site was

caused by grave robbers looking for Confederate

souvenirs to sell.

Life Cycle of Insects

Lt. Col. W. M. Shy, 20th Tenn. Infantry, C.S.A. Born May 24,

1838. Killed at Battle of Nashville, Dec. 16, 1864.

metamorphosis: biological

process in the development

of animals, usually involving

conspicuous changes in the

animal’s form or structure. About

88 percent of all insects go through

complete metamorphosis in four

major stages.

molt: the shedding of an insect’s

outer skeleton during a growth

stage

instar: a developmental stage

of arthropods, generally referring to

changes in the size of the larvae

382 Chapter 13


which it gradually darkens and hardens to form a pupa, the brittle casing from which the adult fl y emerges.

adult, 6–8 mm

12–24 hrs

eggs, 1.2 mm

12 hrs

1st instar, 3 mm

12 hrs

2nd instar, 6 mm

12 hrs

3rd instar, 17 mm

24 hrs

prepupa, 12 mm

2 days

pupa, 9mm

3 days

Figure 13.5 The life cycle of Musca domestica

Forensic Entomology

Knowing the stage of insect inhabitation of a corpse and the duration of stages in the insect’s life cycle can lead to an estimate of the time since colonization. Estimating the time it takes for the insect to fi nd the corpse and start laying eggs allows the investigator to calculate the PMI.

For example, a corpse found with empty pupae of the housefl y tells us only that the time since colonization is more than seven days (Figure 13.5). Suppose, however, that unhatched pupae of another species of fl y are also found, and it is known from laboratory studies that it takes nine days from egg-laying to pupation for this species of fl y under similar conditions. Assuming oviposition within one day of death for both fl ies, the PMI can be estimated to be about ten days.

As a body undergoes successive stages of decomposition, it attracts a succession of different insects; some feed on the products of decomposition, and some feed on the feeders themselves. Like the life cycle of individual insects, the succession of insect predators on a

oviposition: the depositing or

laying of eggs. To oviposit means to

lay eggs.

A vulture boards an airplane, carrying two

dead raccoons. The stewardess looks at

him and says,

“I’m sorry, sir, only one carrion allowed

per passenger.”



corpse follows a predictable pattern, although it is somewhat infl uenced by geography as well as by local conditions. Insect species also vary from region to region, from habitat to habitat, and from season to season.

The Insects of Death

Flies (Diptera) and beetles (Coleoptera) are the two most common orders of insects found on corpses.

Adult fl ies have one pair of wings (see question 15 in Activity 13.1). The larvae appear wormlike. Diptera undergo complete metamorphosis.

Over 1 million species of fl ies are

estimated to inhabit our planet.

Table 13.4: Major Families of Diptera Found On or Near Carrion

Family Examples

Calliphoridae Blowflies such as the blue- and greenbottle flies. In the

early stages of decomposition, often the most abundant

larvae on a corpse. Different species have specific

preferences for oviposition (in shade or light) and

habitat (urban or rural).

Sarcophagidae Flesh flies. These are large flies that lay live larvae

instead of eggs, and may be present shortly after death.

Their larvae eat blowfly maggots.

Muscidae A large family that includes the ubiquitous housefly.

Sometimes found during the later stages of decomposition.

Piophilidae Dark, shiny flies such as the cheese skipper. The larvae

are scavengers and are associated with the late stage of

decomposition.

The heaviest beetle in the world is the

African Goliath beetle, which can weigh

3 ounces and measure 5 inches in

length. The longest beetles in the world

are the long-horned beetles from South

America and Fiji, which attain a length of

about 8 inches.

Beetle adults have two pairs of wings, but the top pair is hard and protects the fl ight wings folded underneath (see question 16 in Activity 13.1). Like Diptera, they have three pairs of legs. The larvae have different shapes and

sizes—some wormlike, some with legs, many soft and C-shaped (grubs); pupae are like pale, mummifi ed versions of the adult. Coleoptera undergo complete metamorphosis. Most beetles are nocturnal and may be found under a body or in the soil surrounding the remains. See Table 13.5.

Blowfl ies and fl esh fl ies arrive at a body fi rst, sometimes within minutes of death, attracted by

the molecules of decay. Later to come are the housefl ies. The female fl y lays eggs within natural body openings and wounds. Inhabitation is a complex

384 Chapter 13


Table 13.5: Major Families of Coleoptera Found On or Near Carrion

Family Examples

Staphylinidae Rove beetles. Can be present within hours of death as well as months later. Adults

and larvae feed on eggs and larvae of other species.

Silphidae Carrion beetles, burying beetles. Example is the sexton beetle, found during the early

stages of decomposition. Adults and larvae feed on maggots as well as carrion.

Histeridae Clown and hister beetles. Present from early on to the start of the dry stage of

decomposition. Adults and larvae feed on maggots and pupae, and on the larvae of

Dermestes beetles.

Dermestidae Skin beetles, hide beetles. Feed on dried skin and tissues during the later stages of

decomposition.

Scarabidae Hide beetles. Some of the last arrivals at a corpse

(dry decay stage).

Cleridae Examples are ham beetles and checkered beetles. These are predators of flies and

other beetles.

Carabidae Ground beetles. Larvae and adults are predatory. Found during all stages of

decomposition.

Tenebrionidae Darkling beetles. Larvae and adults are predatory.

ambient: concerning the

surrounding area or environment

mites: tiny eight-legged

creatures belonging to the order

Acarina, related to spiders and

ticks. Some mites live freely, others

as parasites.

There are 15 board-certifi ed members of the American Board of Forensic Entomology (ABFE) in the United States and Canada. There are only 62 scientists involved in this fi eld of study worldwide.

interaction of different insects and decaying body chemistry.

Fly eggs hatch as maggots that feed only on soft, mushy body parts. Maggots can form large, moving masses that, along with bacterial decomposition, can raise the temperature around them to well above ambient temperature. Maggots account for the loss of most of the body’s mass. Predators, such as ants, wasps, and beetles (hister, rove, and burying beetles), continue to arrive at the scene of death. Beetles feed on the corpse and other arthropods present, and they lay their eggs on or under the corpse. The fi rst fl y families to arrive only like the semifl uid environment, so as the corpse dries, cheese skippers and coffi n fl ies take over. Checkered beetles now arrive to feed on fl ies and other beetles. This feeding frenzy has now reduced the body to 20 percent or less of its original weight, with primarily skin and bones remaining. The fl ies and maggots are gone. The rove beetles remain, and hide beetles arrive. In the soil under the corpse, the number of mites increases. By the end of the decay stage of decomposition, the insects have left, and the corpse has been reduced to about 10 percent of its original weight.



13.2: Body in the Basement

From FBI fi les

In the southeastern United States during mid-November, police were

called to investigate a foul odor that was coming from a small,

single-family home in an impoverished section of town. Investigating

offi cers soon discovered the badly decomposed body of a young, black female

in a shallow grave in the dirt basement of the dwelling.

The victim had died of a single bullet wound to the head infl icted with a

small-caliber rifl e. A careful examination of the corpse and excavation of the

soil in and around the grave site revealed the presence of numerous larvae of

Calliphora vicina (a blowfl y) and larvae and pupae of a relative of the housefl y,

Synthesiomyia nudesita.

Specimens collected from the scene were reared in the laboratory.

Supplemental information including climatic data and soil temperatures was

reviewed in an effort to determine the intervening climatic conditions. Using

information on the developmental biology of both of these species of fl ies,

an estimate was made that the victim had died and was colonized by fl ies

approximately 28 days prior to the time of discovery.

Investigators were able to target their investigation in and around the

estimated time of death. Shortly thereafter, a suspect was identifi ed. This

individual eventually confessed to having killed the victim 28 days prior to the

time the body was found. She had buried the victim in the basement of the

house shortly after committing the homicide.

In this case, the larvae of two species of fl ies provided investigators with the

only scientifi cally reliable method of estimating the time of the victim’s death.

Why were specimens collected at the scene reared in the laboratory? It is diffi cult to characterize fl y species from their larvae, so they are raised to the adult fl y, which is easier to examine and classify. The life cycle for the particular species can then be used to estimate PMI.

Why were data on climatic conditions gathered? Insects are cold-blooded; therefore, their development is temperature-sensitive. Data obtained in lab rearing at 72�F will not refl ect accurate life cycle times at other temperatures; for example, at 62�F, metamorphosis will take longer. There are methods to estimate the effect of temperature on metamorphosis, which we will explore next.

386 Chapter 13


This activity demonstrates the effect of temperature on the rate of

metamorphosis. The data can then be used to explore the concept of

thermal units and their application for estimating PMI. Forensic entomologists use domestic pigs for research because they closely follow human decomposition and are inexpensive and readily available.

Materials• pupae• rearing medium such as

raw liver or ground beef or canned dog food containing beef

• a pint-size clear plastic container with a tight lid or screen

• vermiculite or sterile sand (heated above 100ºC)

• thermometer, or data logger if available

• paper towel• stereomicroscope• ruler• forceps or tweezers• labels and marking pen• nail or awl or a screen• vial with isopropyl alcohol

Procedure

Construct a rearing chamber as follows: 1. Add 1⁄2 inch of vermiculite

or sand to the bottom of the plastic container.

2. Place the rearing medium on a moist, crumpled paper towel occupying about 1⁄3–1⁄2 of the surface of the vermiculite. It is important to keep the medium moist by sprinkling the protruding paper towel with water. (Liver dries out more readily than ground beef or dog food).

3. Punch a number of holes in the lid with a small nail, small enough so no flies can escape, or stretch vinyl screening over the top of the container using a rubber band.

4. The flies will like a bottle cap of water, with a sponge cut to fit in the cap so they don’t drown, and a bottle cap with moist sugar.

5. Place the rearing chamber in areas of different but constant temperature (from 55° to 85°F), where observations can be made on a daily basis.

A rearing chamber

The Effects of Temperature on Rearing of Maggots LaboratoryActivity 13.3

Teacher Note

Ward’s Natural Science sells

pupae of Calliphora and

Sarcophaga. Carolina Biological

Supply sells Sarcophaga bullata as

well as housefl y pupae. Obtaining

two species allows the students

to compare larvae, pupae, and

fl ies as well as their respective

periods of development—a

good illustration of secession.

Allow about 40 days for a full

metamorphic cycle at 80°F.

Extremely valuable in identifying

fl ies and beetles of forensic

importance is a deck of

52 cards, each with a color

photo, information, and a life-

size silhouette of the insect. A

few scientifi c supply houses sell

these for about $35–$40; they

are well worth it.

An example of a time log that

student groups might use for

this activity can be found on the

TRCD (Blackline Master 13.5).

Ask the students to present

their data as a graph, plotting

larvae length (y) against time

(x). Then all the temperature

results can be graphed, time

(y) versus temperature (x).

The representative graphs on

page 388 show what the results

should look like. These can

also be found on the Teacher

Resource CD as Blackline

Masters 13.6 and 13.7.



6. Keep a time log and note when the pupae were received, when they were put into the chamber, when the first and last flies appeared, and so forth. Watch closely for oviposition.

7. Describe (draw or take a close-up photograph) and measure each stage of the metamorphosis.

8. To obtain an accurate length, you must kill the larva by immersing it in alcohol.

9. Note the time of the third instar (when growth levels off and then decreases). Soon thereafter, the maggots will stop feeding, leave their medium, and initiate pupation.

10. Continue recording data until flies emerge (eclosion). 11. Cool the chamber to 32°F or below to immobilize the flies, then pick out

several and kill them in 70 percent isopropanol. 12. Observe the flies under a stereomicroscope and try to identify them. 13. Present the larvae growth data as a graph. Your teacher will collect

growth data for the different temperatures from your classmates so that you can graph the effect of temperature on larvae growth.

14. What conclusions can be made?

eclosion: emergence

of an adult fl y from its

pupal case

Figure 13.6 Common fl ies

c) Calliphora vicinab) Sarcophagidaea) Musca domestica


GO TO www.scilinks.org

TOPIC graphing

CODE forensics2E388

A simple environmental chamber

can be constructed with a lightbulb

in an open cardboard box. The

temperature can be regulated by

moving the top opening.

Teacher Note, continued

18

16

14

12

10

8

6

40 2

Time, day number

Larv

ae L

eng

th, m

m

Larvae Growth

1 3 54 6 7 8 9 10 11

10

9

8

7

6

5

4

3

2

1

010 20 30 40

Temperature, degrees Centigrade

Tim

e o

f 3rd

Inst

ar, n

um

ber

of d

ays

Effects of Temperature on Growth

388 Chapter 13

kh00116_CH13.indd Page 388 8/23/08 12:08:01 AM u-s082kh00116_CH13.indd Page 388 8/23/08 12:08:01 AM u-s082 /Volumes/110/KHUS021/indd%0/Ch 13/Volumes/110/KHUS021/indd%0/Ch 13

Temperature Dependence: Degree-DaysInsect development is dependent upon temperature. As you noted in Activity 13.3, the higher the temperature, the faster the growth. However, while an insect will not develop below a threshold temperature, above a certain temperature its development also stops. Within the development temperature range, however, insect growth is regulated by the amount of thermal energy absorbed, or, simply, per unit of heat. Growth rate is expressed in temperature-time units such as a degree-day or degree-hour. Accumulated units represent the energy needed to effect a change from, say, eggs to the third instar.

Refer back to Figure 13.5. Assuming a constant temperature of 68°F, it takes 36 hours to grow from eggs to the third instar, or 36 � 20°C (68°F) � 720 accumulated degree-hours (ADH). This is the total amount of energy required to effect this change for this particular species of fl y. At 10°C, it will take twice as long to get to the third instar: 720 degree-hours/10° � 72 hours. Theoretically, any combination of time and temperature that adds up to 720 is valid.

How do forensic entomologists use this concept to fi nd a PMI? We will use an example to illustrate the process.

On September 16, two squirrel hunters found a body in the woods under a large oak tree. The forensic entomologist called to the scene found lots of maggots on the body, the largest being 18 mm long. There were also some new prepupae wiggling around the corpse. The forensic entomologist decided that the development stage was the very end of the third instar.

At 3 PM, he recorded an ambient temperature of 74°F. He collected many live specimens and got them back to his lab quickly in order to raise them to fl ies. Several weeks later, he was able to identify them as blue blowfl ies with the disgusting name of Calliphora vomitoria. It took 536 hours at 68°F (20°C) for the collected maggots to

degree-day: a unit of measure

of the energy absorbed by a

biological system, causing growth

Entomologists borrowed the concept of degree-day from agriculturists, who used it to predict certain stages in the growth cycle of plants for timely application of fertilizer or when to spray their fi elds, for example.

Calliphora vomitoria



become adult fl ies. A literature search revealed that this particular species of fl y has a life cycle (from egg to eclosion) of 555 hours at a constant temperature of 27°C, and that it prefers shady places and has a low threshold temperature (temperature below which this fl y is not active).

The forensic entomologist now needed to know the temperatures that the corpse experienced during its stay under the oak tree. A remote weather station was located about 3 miles from the site of the corpse. As with most such stations, it recorded maximum and minimum temperatures each day. These temperatures are shown in Table 13.6.

Table 13.6: Weather Station Log

Date Maximum Minimum Median

Sept 1 76 62 69

2 78 66 72

3 79 69 74

4 80 72 76

5 78 70 74

6 77 71 74

7 76 70 73

8 74 68 71

9 74 66 70

10 76 68 72

11 75 69 73

12 76 68 72

13 74 64 69

14 76 68 72

15 78 68 73

16 76 66 71

17 74 62 68

18 72 60 66

19 70 60 65

20 70 58 64

Silver Falls Weather Station [NWS-467R]

Temperature Log for September 2007

Temperature, °F

390 Chapter 13


Now, how does our forensic entomologist estimate PMI? The fi rst step is to convert the available data to accumulated degree-hours (ADH).

published life cycle: 555 hours � 27°C � 14,985 ADH

lab study: third instar to eclosion: 536 hrs � 20°C � 10,720 ADH

thermal energy needed from eggs to third instar: 14,985 � 10,720 � 4,265 ADH

The average median temperature for the fi rst 20 days of September � 70.9°F (21.6°C); therefore:

4,265 ADH/21.6°C � 197 hours (8 days, 5 hours), the amount or time since the bluebottle fl ies deposited their eggs on the body. This would be September 8 at 10 AM.

But the body was in the woods for about eight days before it was found; thus, the average of the median temperatures from September 8 to September 16 should be used. Will this make a signifi cant difference?

Some entomologists subtract the base or threshold temperature before calculating ADD or ADH, but the species of fl y must be known, and even then the reading is an approximation. When temperatures are close to the lower limit, this calculation can become important.

All these calculations do not account for the time it takes for fl ies to fi nd a body. Sometimes they arrive within minutes, depending upon the location, amount of blood, and temperature. So calculations such as these give only the minimum PMI. What other variables might skew the results?

The weather station was 3 miles from the corpse. Would the temperature have been the same at both places? Perhaps the station was in a sunnier location. To check, our forensic entomologist would have left a temperature recorder at the site for 4–5 days and then compared its readings to those from the weather station. Suppose the site temperature readings were as follows:

1.

2.

3.

4.

•

A remote weather station

Teacher Note

The answer is no. Using the more

accurate median temperatures

makes the approximate time

of death two hours later,

September 8 at 12:00 noon.



The time for the fi rst fl y to fi nd the body was an estimate. The more blood, the faster the fl ies’ arrival.

The part of a body exposed is a factor; for example, the liver, heart, and lungs are choice sites for fl ies. Burn victims also attract fl ies more quickly.

Sometimes clothes can retard colonization. How about insect repellent? Burial, water, and plastic coverings may also delay oviposition.

Maggots feed in masses that generate their own heat. It has been recorded that the temperature of a maggot mass can be well above

ambient temperature. This would tend to accelerate decay.

Toxins and drugs consumed by the person can sometimes accelerate, sometimes retard decomposition. Indeed, traces of drugs have been found in maggots feeding on bodies. We will explore this topic later.

HabitatFly species can vary geographically according to climate, season, and habitat. For example, in the summer, green blowfl ies of the genus Phaenicia are common, whereas in the fall, bluebottle fl ies, Calliphora, are prevalent. Insects found in urban settings, such as Calliphora vicina, may differ from those in the countryside, like Calliphora vomitoria. Some fl y species prefer warm weather, such as the hairy maggot blowfl y Chrysomya rufi facies; others are more active at cooler temperatures. Some like sunlit areas, like the greenbottle fl y Lucilia illustris; some prefer shade, such as the black blowfl y Phormia regina. (See Figure 13.7.) Some fl ies are not active at night. An experienced forensic entomologist can use this knowledge, for example, to corroborate fi eld evidence, infer postmortem movement of a corpse, or even infer prior burial, freezing, or wrapping of a body. Each case is unique due to the high number of variables involved.

•

•

•

•

•A mass of maggots feeding on a corpse sounds like a bowl of Rice Krispies after pouring on the milk.

Date, September Max Temp, °F Min Temp, °F

17 72 60

18 70 58

19 68 58

20 68 56

How would these readings affect the estimated time of death?

Teacher Note

It would make it earlier in the

day by 9 hours, or 3:00 in the

morning. Most fl ies are not

active at night. Had oviposition

occurred before twilight on the

7th, the life cycle would have

begun then; more than likely,

the fl ies found the corpse at fi rst

light on the 8th, so best estimate

of TOD is between 8 PM, 9/7, and

6 AM, 9/8. There is an exercise

for determining

PMI using ADH

at www.nlm.nih.

gov/visibleproofs/

education/

entomology/index.

html. Ward’s

Natural Science

has a nice lab activity on the

same subject: “Critters on

Cadavers.”

392 Chapter 13


a) Phaenicia sericata b) Chrysomya rufi facies

d) Phormia reginac) Lucilia illustris

Figure 13.7 Flies

Fly Infestation as a Function of Habitat LaboratoryActivity 13.4

Do different fl ies have different preferred habitats? Are there different fl y

species in your testing area? Can you identify them?

Materials• raw beef liver, 30–50 g• plastic container, 1 qt or

larger, with tight-fitting lid• sand or vermiculite (the latter

is better)• thermometer• masking or duct tape

• killing vial with isopropanol• ruler• stereomicroscope• labels and marking pen• forceps or tweezers• flypaper trap




Trap and rearing container (fl ypaper stuck to outside of container)

Procedure

1. Punch holes in the sides of the plastic container to allow access to flies while keeping rainwater out. Paper-punch-size is good.

2. Place the meat on a crumpled, wet paper towel, then place both on the sand or vermiculite.

3. Insert the thermometer through a hole in the side of the container into the sand. 4. Place containers outside, one on or near the ground in a consistently shady

area, another in a sunny area. 5. Anchor them by using long nails punched through the bottom of the

container into the soil or by some other means that won’t inhibit sampling, like with a rock on top.

6. Another container should be placed outside on a windowsill. Try to anchor this one also so that birds won’t disturb it.

7. Another container can be placed inside, away from any windows; under an exhaust hood is a good place, as the container will smell.

Teacher Note

Larvae to the inexperienced

observer without a good

microscope all look about the

same. However, the posterior

(big) end of a maggot has

distinctive features that

differentiate species as

well as identify the stage of

development.

Fly traps should be rigid, and can

usually be found in a hardware

or super store. Cut a 2-inch

square and mount it vertically

near the container.

394 Chapter 13



8. Place a fly trap near each habitat; collect any flies, examine them, and compare them with those that have hatched.

9. Record temperature and insect activity each day as often as you can, starting when each container is first put out. A data logger can record temperature and humidity hourly.

10. Look for eggs, maggots, and pupae, taking a sample at each stage of the life cycle and immersing it in alcohol so that it can be measured and described. Remember that the prepupal and pupal stages will be in the vermiculite.

11. Calculate degree-days/hours for each size or stage. 12. Any time after maggots become apparent, cover the holes in the container

with tape so the hatched flies cannot escape.

Analysis Questions

1. Identify the flies from identification cards or photographs.2. Compare the data with those from the other habitats. Explain any differences. 3. Why can’t identification be made from larvae alone?

BeetlesAs mentioned earlier in the chapter, fl ies arrive fi rst at a corpse; then the maggots take over and stay until most of the soft, mushy parts of the body are consumed. Some beetles (Table 13.5) may appear soon after death to feed on the maggots. As the body dries, different families of beetles arrive. They are generally nocturnal and may be found under the remains.

Beetle Infestation of Carrion LaboratoryActivity 13.5

Materials• slab of raw liver, 20–40 g• plastic container, 1 qt with

a lip • nails

• stereomicroscope• forceps or tweezers• killing vial with alcohol• ruler




Liver after several days

Procedure

1. Place the liver on the ground and cover it with the plastic container turned upside down. Punch holes in the sides to allow access to flies. Insert nails through the lip into the ground to anchor it and protect the sample from predators.

2. Allow the container to sit for a few days before removing it.3. Note any activity on top of the meat before gently lifting it up to observe

what may be going on underneath it. Be sure to check in the soil also.4. Continue your observations for several weeks. We are more interested in the

activity of beetles than of flies and their larvae.Some beetles feed on fly larvae (like the Staphylinidae), some on carrion (Dermestidae), some on both larvae and carrion (Histeridae and Silphidae), and some on other beetles (Cleridae and Carabidae). Capture different arthropods and kill them in alcohol for examination and identification.

396 Chapter 13



f ) Hide beetle, Trox sp.e) Red-legged ham beetle, Necrobia rufi pes

c) Clown beetle, Hister nomas d) Sexton beetle, Nicrophorus hybridus

b) Dermestid beetle, Dermestes maculates

a) Rove beetle, Staphylinidae

Figure 13.8 Beetles



The presence of wounds can often be observed by maggot activity away from the usual body orifi ces. For example, activity on the forearms and palms of the hands would imply defensive wounds, probably from a knife attack.

Insects can place a suspect at the scene of a crime. For example, a murder suspect had chigger bites like the ones investigators got at the crime scene. The chiggers were found to be localized to that one area, yet the suspect denied he had ever been there.

Contraband traffi cking can sometimes be traced by identifying trapped insects. For example, marijuana shipments seized in New Zealand contained nine species of Coeloptera (beetles) and Hymenoptera (bees, wasps, ants). Only one of the species was native to New Zealand. The others were found to live in other specifi c areas and habitats, allowing for location of a probable source of the marijuana.

The species of insects plastered on an automobile radiator allowed investigators to refute a suspect’s alibi.

The presence of drugs in a body can sometimes be detected by harvesting and testing the feeding maggots.

In civil cases, insects found in stored food products or clothing can cause considerable discomfort as well as monetary losses. Structural entomology involves damage to buildings such as from termites and carpenter ants.

•

•

•

•

•

•

Other Uses of Insects in Forensic Science

A chigger

A carpenter ant

398 Chapter 13


Maggot Ingestion of Drugs from a Corpse

Flesh-eating insects have been found to have drug residues in their

fl esh as well as in their puparia. This allows examiners to sample for

drug use in a corpse long after stomach contents, urine, and blood have

disappeared. This activity simulates such a drug analysis and explores the

effect of certain chemicals on metamorphosis.

LaboratoryActivity 13.6

puparia: cases

formed by the hardening

of the last larval skin

in which the pupa is

formed. Color starts out

white and turns brown

with time. Singular:

puparium.Materials

• Ground beef, 40–60 g• Fly pupae • Benadryl (diphenylhydramine

hydrochloride), ferric chloride [FeCl3 · 6H2O], potassium ferrocyanide [K4Fe(CN)6], potassium thiocyanate [KSCN], 2 percent cobalt thiocyanate solution [Co(SCN)2]

• clear plastic container, 1 qt, with a few small holes punched in the top, or cover the top with a screen

• vermiculite or sterile sand (heated above 100°C)

• spot plate• Beral pipette• a small killing vial with

alcohol

Procedure

The teacher may assign one of the four “drugs” to each investigative group and the control (no “drugs”) to another group. 1. Make up a small amount of a

saturated solution of one of the chemicals listed above. Mix about 1–2 cc into the sample of ground beef. Mix it well to evenly distribute it.

2. Place the meat on a moist, crumpled paper towel in the plastic container on top of about 1⁄2 inch of vermiculite or sand. Add water and sugar as described in Activity 13.3.

3. Label each container. 4. Add ten or so pupae. 5. Place each container in a

warm spot. 6. Observe what is happening. When you are sure that the flies have laid their

eggs or if maggots can be seen, let the flies out and remove the sugar and water. If the meat dries out, sprinkle a little water on the towel.

A pupa

Teacher Note

See pages 191–193 in Chapter 7

where many of these chemicals

were used.




A description is needed of the habitat, and of whether conditions are sunny, shady, or cloudy.

Climatological data at the site would include temperature, humidity, evidence of rain, and weather data for a period spanning from 1–2 weeks before the victim’s disappearance to 3–5 days after the body is discovered. Temperature should be recorded of the ground by the body and beneath the body, and of the maggot mass.

All the different types of insects on the body, in the body, beneath the body, and fl ying over the body should be collected and labeled. Collection of the largest larvae is most important. Why? Live maggots should be packed carefully so that they can be reared in order to identify them and determine degree-days.

Figure 13.9 summarizes collection requirements at the location of the corpse.

7. When the larvae reach the post-feeding stage (third instar) and are found in the vermiculite or sand, drop half of them into the killing vial. Allow the remaining ones to reach eclosion. Later, harvest the empty pupae and test for drugs in the same way that you did for the larvae.

8. Crush the larvae in the vial, and allow the alcohol to evaporate. 9. Add a small amount of hot distilled water and mix. 10. Take up a few drops of the maggot soup and place it in a well of the spot plate. Each investigative group should also add its sample to the spot plate. Color spot tests will be used to confirm the presence of the “drug.” Benadryl reacts with cobalt thiocyanate solution to form a deep blue precipitate; ferric chloride reacts with potassium thiocyanate solution to make a bright red color; the thiocyanate reacts with ferric chloride solution to make a red color; potassium ferrocyanide reacts with ferric chloride solution to make a deep blue color. The control should be placed in four separate wells of the spot plate and tested with each of the four reagents. No color should show.

Analysis Questions

1. Record the results of the study in your notebook, and assess any problems that occurred.

2. Which test gave the best results? Why?

Collection of Evidence

Teacher Note

Flinn Scientifi c has a nice lab

activity simulating insects

feeding on drugs in a body.

400 Chapter 13


Figure 13.9 Collecting insects for forensic investigations

New Developments in Forensic Entomology

It must be remembered that the PMI is an estimate based upon many variables; not all experts agree. See, for example, www.courttv.com/trials/westerfi eld/timeline/time_of_death.html and www.timeshighereducation.co.uk/story.asp?storyCode�151843&sectioncode�26, for two murder trials where very famous forensic entomologists disagreed on the PMI. Clearly, more research needs to be performed.

DNA is an important tool in many areas of forensic science, forensic entomology notwithstanding. DNA fi ngerprinting of adult fl y species can be used to identify eggs and early-instar maggots. Computer modeling of the life cycle of fl ies may decrease the effect of the number of variables and unknowns in estimating PMI. A forensic entomologist named Arpad Vass has been analyzing the chemicals released into the soil and air from aging corpses in an effort to refi ne the PMI. A trend is also apparent in

Use astandardinsect netOR

Make a smallhand net fromstiff wire andcut-off pantyhose

HAND NET

SOIL/FAUNA

SAMPLE

SPECIMEN

JAR LABEL:

EQUIPMENT

1. Hand Net2. Forceps & Trowel3. Thermometer4. Vials, Jars,

Plastic Bags

SUPPORTING DATA

NEEDED

1. Previous weatherfor area

2. On-site weatherdata (5–7 days)

3. Photos/video ofcrime scene

4. Record time ofcollecting

Collect flying

insects over

corpse with

hand net

Take temperature

of air and of maggot

massTake 3 or 4 soil

samples (a handfuleach) from under

corpse (refrigeratebut do not freeze)

Sample atleast 10cm deep

Secure,ventilatedtin

Location:Date/Hourof collection:Case No.:Sample No.:Detail:Collector:

Label as perspecimen jarlabel

Preserve most maggots(a range of sizes and types)in 70% ethyl or isopropylalcohol

Collect about 2 dozen maggotsand pupa. Keep maggots andpupa separate. Keep hairy andsmooth maggots separate.Place all in a cooler or fridge.Do not freeze.

Maggots concentratein head and open woundsfirst—also at corpse/ground interface

Collect beetlesfrom on andunderneathcorpse

Look for insect specimens(particularly maggots) infolds of clothes, here and

at autopsy

MAGGOT

FLY PUPA

Fly pupa are seed-like,about 1/2 cm long, andred to dark brown in color

Label as perspecimen jarlabel

Maggotscrawl awayto pupate.Look underobjects 3–10 mfrom corpse forpupa.

Kill and preserve

adult flies in fluid

as with maggots

BEETLES



In the summer of 1976, Chicago police raided the apartment of three

suspected drug dealers. These men fi gured that two men living below

them had turned them in, so they killed them. Their bodies were

dumped in the basement of an abandoned building, one inside

a trunk and the other wrapped in a blanket and carpeting. The

suspected drug dealers were charged with murder.

Three years later, when the case was fi nally ready for trial, the

state’s attorneys needed to corroborate the time of death. A

professor from the University of Illinois, Bernard Greenberg,

was called on to help. But all he had to work with were a few

black-and-white photographs that showed the victims covered

with post-feeding larvae and a few pupae. The pupae were light-

colored, implying that they were fresh, not old. Dr. Greenberg

surmised that the insects were Phaenicia sericata because it was

a common carrion fl y in urban Chicago. He performed research to

obtain ADH data for the development of the life cycle of several

fl y species at four different temperatures. He then used

temperature data from the nearest weather station to the crime

scene at the time of the crime in order to adjust his ADH

data. He calculated the time of death to within 21⁄2 days of the actual

shooting—from three-year-old photographs and his research.

His testimony at the trial confi rmed that of one of the state’s key

witnesses (one of the three drug dealers—not the most reliable of

witnesses). The men were convicted of murder and sent to prison.

A similar case occurred in 2006. In 1959, Stephen Truscott, then

14 years old, was convicted of murdering his schoolmate and friend,

13.3: PMI Determined from Photographs

Abandoned building

forensic entomologists joining forces with botanists and anthropologists to evaluate evidence at the scene of death.

On a shorter time scale, research is aimed at improving the measurement of relevant body temperatures in algor mortis. Also, there may be a relationship between the electrical conductance of tissue and the time since death. At one time it was thought that the potassium level in the vitreous humor of the eye was related to postmortem interval; now, mathematical modeling may be used to refi ne this method of measurement.

As with most new developments in forensic science, the Daubert ruling must be satisfi ed. This is especially true in forensic entomology.

402 Chapter 13


Lynne Harper. Evidence consisted of an erroneous eyewitness account of

where they were last seen together and the pathologist report that death

occurred precisely between 7:15 and 7:45 PM, based on stomach contents.

Truscott was convicted of murder. His death sentence was later commuted,

and he was released on parole after serving ten years.

Forty-seven years later, a forensic entomologist from Michigan State

University, Prof. Richard Merritt, examined photographs of the body and data

on the maggots’ measurements that were recorded at the time. From the size

of the maggots, he was able to conclude that Harper’s time of death was not

in the early evening before dark when Truscott was last seen with her, but

after dark or the next morning when Truscott was home or in school. As a

result, his conviction was set aside, but the court was not able to declare his

innocence because of legal technicalities.

Dr. Richard Merritt



Answer the following questions. Keep the answers in your notebook, to be turned in to your teacher at the end of the unit.

1. On page 380, some of the chemicals that contribute to the odor of a decomposing corpse are listed. A living person does not contain such compounds. Where do they come from, i.e., what is the starting material?

2. Why is it important to know what chemicals are produced in the body as decomposition proceeds?

3. The time of colonization is used to describe insect activity in a body. Is this the same as the postmortem interval? Explain.

4. What are the two insect orders most commonly found on a decaying corpse?

5. In an experiment, you know that you have to deal with three variables. How do you proceed?

6. Prepare a dichotomous key for sorting and identifying a set of common objects, such as screws or paper clips.

7. Was the “potato corpse” activity (page 377) representative of algor mortis? Explain.

8. Sometimes remains are preserved on purpose, sometimes by accident. Name at least two examples of each.

9. What are the four principal stages of metamorphosis of Diptera? Why are they important to forensic entomology?

Checkpoint QuestionsAnswers

1. amino acids

2. Refer to Vass’s work on p. 401.

3. No, there is an interval between death and the fi rst

oviposition that can naturally range from minutes

to even days under certain circumstances.

Freezing, burial, and drowning are types of

conditions that can also delay infestation.

4. Diptera and Coleoptera

5. Run the experiment keeping two of the variables

constant and look at the outcome. Repeat, always

keeping two of the parameters constant.

6. One would expect to separate, say, screws by type

(wood, sheet metal), then description (fl at head,

round head), then material (steel, brass, chrome),

then size.

7. The answer depends on experimental results.

8. Egyptian burials, “bog bodies,” Inca mummies of

Peru, Oetzi, Col. Shy

9. Egg, larva, pupa, adult. The time required for each

stage can be used to estimate PMI from the

insects found on the corpse.

404 Chapter 13


10. A body is found still warm, but with rigor mortis. What is the estimated time of death? How could you be more exact?

11. Why is it important to know what kinds of fl y larvae inhabit a corpse?

12. What are the variables that affect the period of development of a particular species of fl y?

13. What do beetles have to do with estimating the PMI?

14. The ADD for the complete life cycle of Sarcophaga bullata has been observed to be 37 days at 27°C. What would it be at 18°C?

15. A fully clothed male was found, facedown, in the basement of a house at 8 AM on July 17. There was a maggot mass in his back, and infestations were apparent in his mouth and nose. The temperature in the basement was 70°F. The house was closed up,

Photograph of a fl y reared from the corpse

Answers, continued

10. Dead for 3–8 hours. Take the temperature; use the

Glaister equation.

11. Different species of fl ies require different times to

develop, which is related to determining PMI.

12. temperature, drugs, predators

13. As with fl ies, there is a somewhat predictable

succession of beetles devouring a corpse or its

inhabitants, depending on the stage of death;

thus, a time sequence can be established.

14. 551⁄2 days: (37 � 27)/18

15. It took 36 hours at 75°F (23.9°C) to raise eggs to

12 mm; 36 � 23.9 � 860 ADH. Dividing by the

temperature in the basement of 70°F (21.1°C)

gives 41 hours for the oldest larvae to grow

from oviposition to 12 mm. Counting 41 hours back

from 8 AM on July 17 gives a TOC of 3 PM, July 15.

The PMI was estimated to be about 15 minutes

earlier because it was noted that there were

fl ies in the house, so it would not have taken

long for them to smell the blood. The insects are

Musca domesticus, the common housefl y with

its characteristic four stripes on the thorax (see

p. 371, question 15, and Figure 13.6, p. 388),

and a sexton beetle, which looks very similar to

the one in Figure 13.8. Normally, a blowfl y would

fi nd the corpse fi rst if it were outside, but the

housefl ies had the advantage in the closed house.

The Silphidae beetle is an early visitor to a corpse,

feeding on both larvae and carrion; the dirt fl oor

would allow it to live indoors. The development

time for the fl ies was consistent with that of

Musca domestica (see Figure 13.5). The maggot

mass in the back of the victim implies a wound in

the back, which would be evident at autopsy.



yet there were a lot of housefl ies buzzing here and there. The forensic entomologist collected about 40 of the largest maggots, from 10 –12 mm long. She did not see any puparia; however, there were two beetles under the body. The temperature in the basement was monitored for the next fi ve days and found to be very stable at 70°F.

Back at the lab, half the maggots were placed in an incubator at 75°F at 9 AM. Flies started emerging from their pupae about 71⁄2 days (180 hours, to be exact) after incubation of the larvae. The forensic entomologist identifi ed the fl y and let it run through its life cycle. She found that it took 36 hours to grow larvae 12 mm long.

What did she estimate the time of colonization (TOC) to be? The PMI? Identify the two insects shown. Is their presence consistent with the estimated PMI? Explain all your reasoning as if you were in court.

16. Why was the body of Col. Shy so well preserved? What other methods of preservation have been used on bodies?

17. Dr. Merritt used data on the size of the maggots on Harper’s body to estimate PMI. What else would he have needed in making his estimate?

Photograph of a beetle under the corpse

Answers, continued

16. The arsenic embalming and the lead-lined coffi n

retarded decomposition—interesting in that both

elements hasten death. Egyptian mummies were

eviscerated and dried out with natron. Some

corpses were said to have been “pickled” in

alcohol to preserve them. In modern times, bodies

are kept frozen with liquid nitrogen in the hopes

that they may be “revived” in the future.

17. the species of fl y; weather conditions, especially

temperature; time of day the body was found

406 Chapter 13


Additional Project

It is known that maggots, even puparia, will contain drug

metabolites as a result of feeding on the drug user’s body. Does

this apply to beetles that devour body parts during the later

stages of decomposition? Follow an appropriate procedure, but

substitute for the rearing medium a portion of dried roadkill,

pigskin, a dried-out pork chop, or a piece of leather. Pierce it

while it is being soaked overnight in a solution of the “drug”

that worked the best in Laboratory Activity 13.4. Oven-dry it and

place it in a container with dermestid beetles that your teacher

has supplied. Add some wood chips or pieces of bark and a

small piece of cotton or filter paper that has been dampened.

After the dried meat has been consumed, harvest some of the

beetles and test for a color reaction.

Dermestid beetle

Books and ArticlesBass, J. Carved in Bone: A Body Farm Novel. New

York, NY: HarperCollins, 2006.

Catts, E. P., and N. H. Haskell. Entomology and

Death, a Procedural Guide. Clemson, SC: Joyce’s

Print Shop, 2000.

Goff, M. L. A Fly for the Prosecution. Cambridge,

MA: Harvard University Press, 2000.

Sachs, J. S. Corpse. New York: Basic Books, 2001.

Sachs, J. S. “A Maggot for the Prosecution,”

Discover, November 1998, p. 103.

Gannon, R. “The Body Farm,” Popular Science,

September 1997, p. 77.

Schoenly, K. G., N. H. Haskell, D. K. Mills,

C. Bieme-Ndi, K. Larsen, and Y. Lee. “Using

Pig Carcasses as Model Corpses,” The American

Biology Teacher, Vol. 68, 2006.

Carloye, L. “Of Maggots and Murder: Forensic

Entomology in the Classroom,” The American

Biology Teacher, Vol. 65, 2003.

Websiteswww.amonline.net.au/insects/insects/resources.

htm#forensic; many good links

www.forensicentomology.com/introduction.htm; a very

complete exposure to forensic entomology

http://research.missouri.edu/entomology; more links

www.nhm.ac.uk/nature-online/life/insects-spiders/

webcast-forensicentomology/forensic-entomology.

html; video explaining forensic entomology

References



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kkh00116 CH13.indd Page 368 8/21/08 4:51:15 PM ... · Forensic Entomology Chapter 13 368 ... presentation, which is an overview of the chapter. It can be used as introductory material